This application claims the priority of German Application No. 101 58 872.0-1 filed Nov. 30, 2001, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an internal combustion engine having an injection valve, and to a method for operating an internal combustion engine of this type.
In order to maintain the minimum possible exhaust emissions from an internal combustion engine, it is possible to influence the combustion performance of the fuel in the cylinders of the internal combustion engine by forming the optimum possible mix. Particularly during the warm-up phase of the internal combustion engine immediately after the engine has been started in the cold state, it is often impossible to achieve low levels of emissions. These problems can be avoided if starting fuel, which is more readily flammable than the fuel used for normal operation of the internal combustion engine, is provided separately.
German Patent DE 42 15 959 C1 discloses a fuel supply system of this type in which, during the warm-up phase, readily flammable gaseous fuel fractions are supplied from a storage tank. In this case, the starting-fuel fractions are metered into the intake line of the internal combustion engine as a function of operating parameters of the internal combustion engine, such as engine speed, coolant temperature or warm-up temperature.
German Patent DE 196 33 259 A1 proposes a fuel vaporizer for an internal combustion engine, which is additionally provided for individual injection into the cylinders and has a downstream fuel separator which separates low-volatility fuel constituents out of the fuel vapour, in order to prevent the fuel vapour from being condensed back into the lines which carry fuel vapour. However, the known measures are only intended for the warm-up phase of the internal combustion engine, requiring a relatively high structural outlay.
An object of the present invention is to provide an internal combustion engine and a method for operating the internal combustion engine having improvements in the exhaust emissions and in the operating performance of the internal combustion engine achieved over the entire operating range of the internal combustion engine.
According to the invention, for each cylinder of the internal combustion engine there is one injection valve and, in addition, there is at least one port injector at the intake tract of the internal combustion engine. The port injector has two supply inlets, which can be closed off by the control unit and having the first supply inlet connected to a device for preparing starting fuel and the second supply inlet connected to a fuel tank. Suitable injection valves are provided in particular induction port valves or direct injection valves. During the warm-up phase of the internal combustion engine, the port injector delivers starting fuel which is provided by a preparation module connected to the supply inlet of the port injector. In higher load ranges of the internal combustion engine, additional fuel is delivered by the port injector via the second supply inlet, so that the total quantity of fuel which is to undergo combustion can be metered proportionately via the injection valves and the port injector. Therefore, according to the invention, both the starting fuel and the fuel for normal operation, i.e. two different types of fuel, can be metered using one injector and therefore with a low structural outlay. The bi-fuel port injector with two supply inlets is preferably positioned downstream of the electronic throttle valve control device, as seen in the direction of flow in the intake tract, or, in V-engines or similar engines, such as W arrangements, at the junction of the different cylinder banks.
The total quantity of the fuel which is to undergo combustion in the cylinder is preferably metered proportionately by the injection valves and by the port injector. The control unit determine the quantitative proportions which are to be delivered by the port injector and the injection valve of the corresponding cylinders. The benefit results, in particular, when the internal combustion engine is operating in relatively high load ranges, in which a basic quantity of the total amount of fuel, which is to undergo combustion, is metered in via the port injector, and the quantity of fuel required for combustion is topped up by the sequentially actuated injection valves. Therefore, the injection valves can be designed for lower quantitative flow rates, with the result that more accurate metering of injection is possible in idling mode or at low engine speeds. Furthermore, smooth running of the engine and the control quality of injection can be improved. Moreover, the internal combustion engine has better cold-starting properties, since the smaller opening gaps of the injection valves make it possible to set an optimum form for the jet of fuel injected into the combustion chamber. The reduction in the Sauter diameter causes the fuel to evaporate more quickly, and, as a result, the mixture formation and the combustion are improved. The advantages of optimum control of the fuel injection with smaller delivery quantities from the injection valves are particularly clear in internal combustion engines whose injection valves are fed with fuel from a common pressure line (common rail injection).
During the warm-up phase, the internal combustion engine is preferably operated with a lean mixture so that a further contribution is made to reducing the exhaust emissions during a cold start. Furthermore, if the mix formed in the warm-up phase is lean, the exhaust gas is heated to a lesser extent, so that it is possible to dispense with a secondary air system which is required for warming up with a rich mix being formed. The manufacturing costs of the internal combustion engine can be reduced considerably by dispensing with the fitting of relatively large secondary air pumps and also device at the engine/cylinder head, such as switching valves, hoses, or secondary bores in the cylinder head.
The reduction in the untreated emissions may make it possible to do without catalytic converters arranged immediately adjacent to the internal combustion engine in order to comply with the statutory exhaust limits. It is sufficient for catalytic converters to be arranged in the region of the underbody of a vehicle which is driven by the internal combustion engine. In this area, the catalytic converters are subject to less ageing, because the temperatures are lower than in the vicinity of the engine and because the thermal load on the catalytic converters is lower.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.